Photographically sensitive lithographic printing plate



Nov. 6, 1962 l. H. CRAWFORD 3,062,648

PHOTOGRAPHICALLY SENSITIVE LITHOGRAPHIC PRINTING PLATE Filed Feb. 9,1960 U/VHAROENEO OELATl/VO-S/LVER HAL/DE EMULSION OO/V7Al/Vl/V67AN/V/IV6 DEVELOPER HYDROPH/L/C LAYER OF OOLLO/OAL SILICA A/VO METHYL ME7' l-IACRYLATE POLYMER "Ill/ll IA mm //////////Zi PAPER BASE ATTORNEYSUnited States Patent O 3,062,648 PHOTOGRAPHECALLY SENSETIVE LKTHO-GRAPHIC PREN'HNG PLATE Irvin H. Crawford, Rochester, N.Y., assignor toEastman Kodak Company, Rochester, N.Y., a corporation of New JerseyFiled Feb. 9, 195%, Ser. No. 7,712 6 Claims. (Cl. 96-76) This inventionrelates to lithographic printing plates and to methods of making thoseplates, especially paper printing plates. The invention relates to boththe preparation of the lithographic plate and the preparation of ahydrophilic lithographic surface on a paper support requiring noinsolubilizing agent.

One object of my invention is to prepare printing plates of the negativeworking type that is used to make positive copies from negativeoriginals. Another object of my invention is to prepare sensitizedlithographic printing plate having an emulsion thereon which uponexposure and development forms a water repellent oleophilic imagethereon. Another object of my invention is to provide lithographicprinting plates in which the hydrophilic surface employed comprisescolloidal silica and a small amount of a resin binder therefor. Afurther object of my object of my invention is to combine a lithographiccoating mixture with a paper base which is sufiiciently impervious tothe action of Water to substantially resist stretching and shrinking.Other objects of my invention will appear herein.

The providing of a satisfactory hydrophilic surface on a support for usefor lithographic printing plates has been the subject of many patents.The majority of these patents use water absorptive materials such aspolyvinyl alcohol, casein, gelatin, carboxymethyl cellulose, starch, orthe like, as the continuous phase of the hydrophilic layer. Ordinarily,some pigment or filler such as titanium dioxide, clay, or blanc fixe isadded to provide a suitable surface texture. The continuous phase isinsolubilized in some way to prevent disintegration of the layer whenwet under the stresses and abrasive forces of the printing press.Insolubilizing agents which have been employed are formaldehyde,glutaraldehyde, ureaformaldehyde resin, melamine-formaldehyde resin, orthe salt of a bior tri-valent metallic ion such as of copper, iron,aluminum and chromium.

The lithographic printing plate which is the object of this invention ismade by applying to the surface of a Water-resistant support, such aspaper which has been made water-resistant such as by applying a resinouscoating thereto, a hydrophilic layer essentially consisting of colloidalsilica and methyl methacrylate resin emulsion. Over this hydrophiliclayer is then applied a layer of an unhardened silver halide emulsion ofthe type described in U.S. Patent No. 2,675,313 of Yutzy and Yackel. Theprinting plate in accordance with my invention is characterized by thecomplete absence of insolubilizing agents therein which would causehardening of the gelatin of the silver halide emulsion prior to actualexposure and development thereof. The silver halide emulsion usedcontains therein a tanning developer which upon development of theemulsion in aqueous alkaline solution after exposure causes hardening ortanning of the gelatin of the emulsion only in the specific areas wherethe silver is reduced. This leaves a positive image of reduced silverand hardened gelatin while the remaining areas of the silver halideemulsion are soft and unhardened. The unhardened emulsion is thereuponremoved such as by washing with warm water (90-110" F.) revealing thehydrophilic surface underneath but leaving the oleophilic 3,662,648Patented Nov. 6, H952 image on the hydrophilic surface to make asatisfactory lithographic printing plate.

Since the system depends upon absence of hardening of the emulsion inthe non-exposed areas there should be nothing in the base which willharden or promote hardening of the emulsion. Thus, the supports asdescribed in the prior art which involve the use of insolubilizingagents in their preparation would be unsuitable, as those agents notonly insolubilize the hydrophilic adhesive material used in the coating,but also have a hardening effect upon the unhardened gelatin emulsionwhich is applied thereover. The hydrophilic layer in accordance with thepresent invention does not require insolubilizing agent to give abrasionresistance on the press and thus constitutes an improvement overprevious hydrophilic layers.

Referring to the attached drawing the figure illustrates a lithographicprinting plate in accordance with my invention in which a paper base iscoated with a hydrophilic layer of colloidal silica and methylmethacrylate polymer and thereover is applied an unhardenedgelatino-silver halide emulsion containing tanning developer.

The hydrophilic layer employed in accordance with my inventionessentially consists of a colloidal silica dispersion and a polymethylmethacrylate emulsion. The making of a colloidal silica dispersion suchas would be useful in my invention is described in U.S. Patent 2,375,738of John F. White. Colloidal silica dispersions useful in preparinghydrophilic layers in accordance with my invention are sold as aqueoussilica dispersions under the trade names of Syton 200 (solids content onthe order of 30%) by the Monsanto Chemical Company, Merrimac Division,Everett, Massachusetts, and Ludox (aqueous colloidal solution ofhydrated silica containing 30% SiO by the Du Pont Company. The silicaconcentration of the colloidal silica dispersion used can vary such asfrom 1040% or more.

The polymethyl methacrylate in the coating composition employed forforming the hydrophilic layer is supplied in the form of an emulsionthereof such as obtained by the emulsion polymerization of methylmethacrylate as is known in the art. A methyl methacrylate resinemulsion which has been used successfully in coating compositions forthe application of hydrophilic layers in accordance with my invention issold under the trade name Rhoplex AC33 by Rohm and Haas Company. It isordinarily preferred that pigment or filler be incorporated in thecomposition which supplies the hydrophilic layer. Materials such asfinely divided clay, titanium dioxide, barium sulfate, or the like,alone or in admixture have been found to be useful in this connection.The colloidal silica should constitute at least 30% of thesilica-pigment (filler) mixture employed in preparing the hydrophiliclayer composition. In some cases it might be desirable to add athickener to the composition. Hydroxyethyl cellulose is useful for thispurpose. Instead of or in addition to the pigments and fillers listed,materials which might be employed are finely divided glass, sand, quartzor diatomaceous earth. In some cases it might be desirable to add apigment or dye to give a colored coating which may improve resolutionand decrease halation.

ln compounding the materials to form a coating com position the pigmentand/or filler and the colloidal silica should have a ratio to acrylateresin 6:1 to 8:1 dry basis. The composition thus prepared may have asolids content of from 30 up to 50%, although compositions having solidscontents outside of this range may be found to be useful. The conditionsshould be such that a cov erage of the hydrophilic layer dry Weight ison the order of 18-30 grams per square meter.

smas es The emulsion layer is supplied by a composition of an unhardenedgelatino-silver halide photographic emulsion such as described in US.Patent No. 2,675,313, which emulsion contains a small proportion of atanning development agent. Some tanning developers which are useful inthe emulsion composition are various dihydroxy diphenyls,5,6,7,8-tetrahydronaphtho hydroquinone, hydroquinone or pyrocatechol.For the successful operation of the invention the emulsion layer shouldnot be harder than would be in the case with gelatin containing 0.25ounce of formalin (diluted 1:3 with Water) or 0.7 gram of dryformeldehyde per pound when freshly coated or 0.1 ounce of formalindiluted 1:3 with water per pound for a sample aged 3-6 months. Byunhardened and substantially unhardened as used herein, it is to beunderstood that this means a hardness of the order obtained from gelatintreated with no more formaldehyde than listed above.

The support for the layers which make up my invention is paper and it ispreferred that paper made waterresistant to give good dimensionalstability and resistance to stretching and pulling be used. This can beconveniently done by coating formaldehyde-free paper on both sides witha solution consisting of 4% casein and 96% styrene-butadiene copolymerlatex in water to which ammonium hydroxide has been added to adjust thepH to the alkaline side and a Wetting agent such as sodium laurylsulfate has been used to facilitate the application of the coating tothe paper, the solution for producing water resistance containing 30% ofsolids and the dry coverage of the coating on the paper being on theorder of grams of coating per square meter of surface.

The lithographic paper prepared in accordance with my invention isparticularly useful in making positives from negative originals such asfor the making of printing plates from microfilm records.

For instance, the emulsion layer may be exposed to light through a filmnegative or to an opaque negative by reflected light. The exposedemulsion is then activated in an aqueous alkali solution such as a 4%solution of sodium carbonate in water, which solution may contain 10% ofurea and 0.1% of potassium bromide or some other desensitizer. Theadvantage of using a desensitizer is that the finishing of theprocessing might be carried out in ordinary light although the use ofsubdued light might, in many cases, be preferable. During activation ofthe emulsion the silver in the area of the emulsion which had beenexposed is developed by the developer in the emulsion and as thedevelopment proceeds the gelatin is also hardened or insolubilized, butonly in the specific areas where the silver is reduced. This leaves apositive image of reduced silver and hardened gelatin, all the remainingareas thereof being soft and unhardened. By washing with warm water orsome other suitable technique the unhardened gelatin is removed and anoleophilic image is formed on the hydrophilic surface making asatisfactory lithographic printing plate.

The plate thus formed is then suitable for use in a printing process inwhich the plate is first wet with an aqueous fountain solution, theliquid being held by the hydrophilic surface and repelled by theoleophilic image. Next the plate is contacted by inking rollers thegreasy ink adhering to the oleophilic image but being repelled by themoistened hydrophilic areas. Thus, an ink image is formed, which istransferred to a rubber blanket roller from which the image istransferred to a paper sheet.

The following examples illustrate my invention:

Example 1 A composition was prepared comprising clay 90 parts, 312 partsof an aqueous colloidal solution of hydrated silica containing SiO and asmall amount of alkali as a stabilizing agent, and polymethylmethacrylate resin emulsion 65 parts. In forming a coating compositiontherefrom, the clay and colloidal silica were mixed and passed through asuitable colloid mill or homogenizer to disperse the pigment. Thepolymethyl methacrylate emulsion was then added and the mass was mixedwith slow agitation to prevent the entrapment of air, all at roomtemperature. The ratio of pigment (clay and colloidal silica) to binder(acrylate resin) is 6 to 1, dry basis. The total solids content is44.6%, the remainder being water. The completed formula was coated onpaper, stable in Water, at the dry coverage rate of l8-30 grams ofhydrophilic layer per square meter. The coating was dried in a currentof Warm, dry air and was then heated to a temperature of 240 to 270 F.by radiant heaters or other heating device. The heat treatment causesthe acrylic resin to coalesce and form a continuous film thereby holdingthe clay and SiO particles in place and thus providing adequate Wetabrasion resistance. The thus coated paper was overcoated with ahardened gelatin-silver halide photosensitive emulsion of the typedescribed in US. Patent 2,675,313 in the form of a layer of .005 inchthickness. The product thus prepared was useful for preparinglithographic printing plates as described above.

Example 2 The preceding was repeated except that the compositionemployed for the hydrophilic layer consisted for water dispersibletitanium dioxide 90 parts, colloidal silica dispersion (30% Si0 312parts, and polymethyl methacrylate emulsion parts. The ratio of Ti0 andsilica to resin was approximately 6:1 dry weight. A product havingproperties useful for lithographic purposes was obtained.

Example 3 Example 4 A composition for applying the hydrophilic layer topaper as described in the preceding examples was prepared by adding thepolymethyl methacrylate emulsion directly to the dispersion of colloidalsilica, in the proportion of 400 parts of silica dispersion and 43 partsof polyalkyl acrylate emulsion. As a result the mixture had a lowviscosity. Hydroxyethyl cellulose was added thereto as a thickener. Thecomposition thus obtained was coated out onto paper having goodstability in water, which was then overcoated with unhardened silverhalide emulsion as described herein. A product useful for preparinglithographic printing plates was obtained.

Example 5 The above was repeated except that the composition used forthe hydrophilic layer consisted of clay 50 parts, titanium dioxide 50parts, colloidal silica dispersion 30% SiO 835 parts, polyalkyl acrylateemulsion 109 parts, and hydroxyethyl cellulose (4% solution) 160 parts.

5 A product having good characteristics for use in photolithographicprocedure was obtained.

In addition to the ingredients shown in the above formulas, it issometimes desirable to add small amounts of a commercially availableWetting agent or defoaming agent to improve the coating properties ofthe composition. These, however, in no way affect the hydrophilic orlithographic properties of the coatings applied.

It is thought that the hydrophilic coating as described herein functionsin the following manner, but it is to be understood that the inventionis not limited to the conclusions of the theoretical discussion. It isbelieved that the acrylic resin which is present in the hydrophiliclayer as a continuous film is hydrophobic or water repellent and that itdoes not dissolve, swell or take up water on its surface when contactedwith the fountain solutions in printing, but that it provides a toughabrasion resistant film to bind the pigment particles firmly in place.For this purpose some other resin of an alkyl ester of an acrylic acidor methacrylic acid or a styrenebutadiene or styrene-acrylic resin latexwould be useful. The colloidal silica has a very small particle size,the particles being on the order of 15 millimicrons or even less indiameter. Therefore, a large surface area is presented as theseparticles are in discreet or separated form. Once the coating containingthe colloidal silica has dried the silica becomes resistant tore-dispersing but the colloidal silica particles not completely coveredwith binder present a large surface area available for adsorption ofmoisture. It is believed that these fine silica particles adsorbmoisture tenaciously, thus presenting a uniform ink repellent film ofwater to the press inking rollers.

When the pigment to binder ratio is too low the binder completelyencompasses the SiO particles; hence, moisture is not adsorbed. Withthis condition complete inking of the entire plate surface occurs. Whenthe pigment to binder ratio is between approximately 6:1 and 8:1 asspecified herein, the binder spot welds the silica particles togetherleaving a surface of those particles free to adsorb moisture. On theother hand, when the pigment to binder ratio is much above 8:1insufficient binder is present to bind the particles of silica and otherpigment is place and the coating has a tendency to disintegrate in theprinting operation.

The above described sensitized plates make possible a projection speedprocess for making multiple copies from microfilm records. At present,to my knowledge, there has been no other inexpensive means of makingmultiple copies from microfilm negatives.

I claim:

1. A lithographic printing plate, substantially free of gelatinhardener, containing in that order 1) a water resistant support, (2) ahydrophilic layer comprising an inorganic component of colloidal silicaand pigment-filler, the silica constituting at least 30% thereof dryweight, and a water resistant latex resin component, the ratio of theinorganic component to the resin component being approximately 6:1, dryweight, and (3) a layer of a gelatino-silver halide emulsion containingtherein a gelatin tanning silver halide developing agent.

2. A lithographic printing plate, substantially free of gelatinhardener, containing in that order a water resistant paper base, ahydrophilic layer of a mixture of titanium dioxide, clay and colloidalsilica, the latter constituting at least 30% of the mixture, and amethyl methacrylate latex resin component, the ratio of the mixture ofclay, titanium dioxide and colloidal silica to latex resin being withinthe range of approximately 6:1 to approximately 8:1, dry weight, and alayer of a gelatinosilver halide emulsion containing a tanningdeveloper.

3. A lithographic printing plate, substantially free of gelatinhardener, containing in that order (1) a water resistant paper basesupport, (2) a hydrophilic layer comprising an inorganic component ofcolloidal silica and pigment-filler, the silica constituting at least30% thereof dry weight, and a water resistant latex resin component, theratio of the inorganic component to the resin component being within therange of approximately 6:1 to approximately 821, dry weight, and (3) alayer of a gelatino-silver halide emulsion containing therein a gelatintanning silver halide developing agent.

4. A lithographic printing plate, substantially free of gelatinhardener, containing in that order (1) a water resistant support, (2) ahydrophilic layer comprising an inorganic component of colloidal silicaand pigment-filler, the silica constituting at least 30% thereof dryweight, and a water resistant methyl methacrylate latex resin component,the ratio of the inorganic component to the resin component being withinthe range of approximately 6:1 to approximately 8:1, dry weight, and (3)a layer of a gelatino-silver halide emulsion containing therein agelatin tanning silver halide developing agent.

5. A lithographic printing plate, substantially free of gelatinhardener, containing in that order a water resistant paper base support,a hydrophilic layer of a mixture of clay and colloidal silica, thesilica constituting at least 30% thereof and a methyl methacrylate latexresin component, the ratio of the clay and colloidal silica to the latexresin component being within the range of approximately 6:1 toapproximately 8:1, dry weight, and a layer of a gelatino-silver halideemulsion containing a tanning developer.

6. A lithographic printing plate, substantially free of gelatinhardener, containing in that order a water resistant paper base support,a hydrophilic layer of a mixture of titanium dioxide and colloidalsilica, the latter being at least 30% thereof, and a methyl methacrylatelatex resin component, the ratio of TiO and colloidal silica to thelatex resin component being within the range of approximately 6:1 toapproximately 8:1, dry weight, and a layer of a gelatino-silver halideemulsion containing a tanning developer.

References Cited in the file of this patent UNITED STATES PATENTS2,698,235 Swindells Dec. 28, 1954 2,716,059 Yutzy et a1. Aug. 23, 19552,772,166 Fowler Nov. 27, 1956 2,805,159 Unkauf Sept. 3, 1957 2,835,575Cowden et al. May 20, 1958

3. A LITHOGRAPHIC PRINTING PLATE, SUBSTANTIALLY FREE OF GELATINHARDENER, CONTAINING IN THAT ORDER (1) A WATER RESISTANT PAPER BASESUPPORT, (2) A HYDROPHILIC LAYER COMPRISING AN INORGANIC COMPONENT OFCOLLOIDAL SILICA THEREOF DRY WEIGHT, AND A WATER RESISTANT LATEX RESINCOMPONENT, THE RATIO OF THE INORGANIC COMPONENT TO THE RESIN COMPONENTBEING WITHIN THE RANGE OF APPROXIMATELY 6:1 TO APPROXIMATELY 8:1, DRYWEIGHT, AND (3) A LAYER OF A GELATINO-SILVER HALIDE EMULSION CONTAININGTHEREIN A GELATIN TANNING SILVER HALIDE DEVELOPING AGENT.